1. Field of the Invention
This invention pertains generally to ultra-wideband communications, and more particularly to ultra-wideband (UWB) transmitters.
2. Description of Related Art
Ultra-wideband (UWB) wireless communication is based on the transmission of data in extremely short, e.g., 50-1000 ps, pulses spread out over a broad frequency range or bandwidth, typically several GHz, of the electromagnetic spectrum. Large data bursts, e.g., hundreds of Gb/s, are possible because the data are carried simultaneously at a wide range of frequencies across the electromagnetic spectrum.
UWB communications offers many advantages. UWB signals are more difficult to detect than narrowband (essentially single frequency) signals. The combination of broad spectrum, low power, and extremely short pulses also cause much less interference with other devices than do conventional narrowband wireless systems. Also, UWB is much more resistant to electrical interference from other devices than other wireless technology. Thus, UWB's data capacity, speed, low power requirements, and resistance to interference make it attractive as a communications technology.
UWB pulses spread the transmitted energy over many frequencies, over a band of typically several GHz, as opposed to traditional narrowband, which generally operates as a continuous wave at a specific frequency and covers a limited band of about 30 KHz. Cellular phones operate in the wideband, which covers about 5 MHz. UWB bandwidth provides high capacity, resistance to jamming, and low probability of detection. Thus UWB provides an attractive alternative to the other communications technologies. At present, the FCC restricts commercial UWB systems, but Government use is less restricted. UWB appears very promising for the future.
One type of receiver used in UWB communications systems is a delay and multiply receiver in which a received pulse is multiplied by a delayed prior received pulse to increase the magnitude. This requires a precise spacing between the transmitted pulses so that the delay can be chosen so that the presently received pulses are coincident with the delayed previously received pulses. It is also required that the pulses be in phase so that when they are multiplied they do not cancel out.
Thus, it is desirable to provide an UWB transmitter capable of generating a sequence of RF bursts with precise spacing between the bursts.
It is also desirable to provide an UWB transmitter capable of generating a precisely spaced sequence of RF bursts where each burst starts up at the same phase as the other bursts.